Stabilizer links are ball joint parts for connecting a suspension and a stabilizer. FIG. 1 is a perspective view of an approximate structure of a vehicle from the front wheels side. A suspension 10 is provided to right and left tire 30 and has an arm 11 and a cylinder 12. The arm 11 has a lower end portion that is fixed to a bearing portion which supports a shaft of the tire 30. The cylinder 12 is elastically displaceable with respect to the arm 11. The arm 11 is provided with a bracket 13 to which a stabilizer link 200 is fixed. The suspensions 10 support the weight of the vehicle body applied to the tires 30. A stabilizer 20 has a bar 21 with an approximately U-shaped and is mounted to the vehicle body via bushes 22. The stabilizer 20 provides roll stiffness for the vehicle.
One of the stabilizer links 200 is provided to the bracket 13 of the suspension 10, and the other is provided to an end of the bar 21 of the stabilizer 20. The stabilizer links 200 are connected with each other by a support bar 500. The stabilizer links 200 transmit load, which is generated when the suspension 10 receives input power from a road surface, to the stabilizer 20.
FIG. 2 is a cross section that shows a structure of the stabilizer link 200. The stabilizer link 200 includes a ball stud 201, a ball seat 301, a housing 302, and a dust cover 401. The ball stud 201 has a stud portion 210 and a ball portion 220, which are integrally formed.
The stud portion 210 has a tapered portion 211, a sealing portion 212, and a screw portion 213. The tapered portion 211 is formed at an upper end portion of the ball portion 220. The sealing portion 212 has an upper end portion that is formed with a flange 214 and has a lower end portion that is formed with a projection 215. The dust cover 401 has an upper end portion that is formed with a lip 411, and the lip 411 is abutted and is secured to the sealing portion 212 between the flange 214 and the projection 215. The screw portion 213 of the stabilizer link 200 in the side of the suspension 10 is screwed to the bracket 13 of the arm 11. The screw portion 213 of the stabilizer link 200 in the side of the stabilizer 20 is screwed to the bar 21.
The ball seat 301 and the housing 302 form a supporting member for universally and pivotally supporting the ball stud 201. The ball seat 301 is press fitted with the ball portion 220 of the ball stud 201. The housing 302 accommodates the ball seat 301. The dust cover 401 has a lower end portion that is held between a flange 321 at an upper end of the ball seat 301 and a flange 311 at an upper end of the housing 302.
In this stabilizer link 200, in order to prevent the entry of dust between the ball portion 220 of the ball stud 201 and the ball seat 301, it is important to tightly seal the sealing portion 212 of the ball stud 201 and the lip 411 of the dust cover 401.
Nevertheless, in the above stabilizer link 200, when the ball stud 201 is fully swung under low temperature conditions, there is a possibility of occurrence of opening of the lip 401 of the dust cover 400. That is, the lip 411 may be disconnected from the sealing portion 211 and opens as shown in FIG. 3. In conventional techniques, an O-ring is mounted to the lip 411 so as to ensure sealing characteristics. In this case, the O-ring is provided as a separate member, whereby the production cost is increased.
In regard to this, as shown in FIG. 4A, a technique of providing a side lip portion 412 to the lip 411 of the dust cover 401 has been developed. In this technique, the side lip portion 412 is abutted on an outer circumferential portion of the flange 214 of the ball stud 201 when the dust cover 401 is fitted. The outer circumferential portion of the flange 214 may be extended in the direction of the leading end of the axis and may have a sharp-edged end. In this case, when the dust cover 401 is fitted, as shown in FIG. 4B, there is a possibility that the side lip portion 412 contacts the edge of the outer circumferential portion of the flange 214 and is folded down. Therefore, high assembling productivity cannot be obtained in a mass production line.
In order to prevent the folding down, a technique of forming a tapered portion at the outer circumferential portion of the flange 214 of the ball stud 201 is suggested (for example, WO2006/098124). Specifically, in the technique disclosed in WO2006/098124, the tapered portion is inclined so that the diameter thereof expands from the root to the outer circumferential portion of the flange in the axial cross-section. In this case, the side lip portion of the dust cover has a shape corresponding to the shape of the tapered portion.
However, in the technique disclosed in WO2006/098124, occurrence of the folding down can be prevented, but the flange of the ball stud and the side lip portion of the dust cover are not tightly sealed. Meanwhile, in view of reduction of environmental burdens of vehicles (increase of fuel efficiency) and improvement of motion performance, reducing the weight of vehicle parts is strongly desired. The conventional techniques have not responded to the requirement sufficiently.